Method of cutting quartz



Patented Dec. 2, 1941 METHOD OF CUTTING QUARTZ Charles E. Johnson,Collingswood, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application September 30, 1939, Serial No.297,410

6 Claims.

This invention relates to the art of cutting natural quartz crystals (orrock crystals as they are sometimes called) and has for its principalobject to provide (a) a simplified, inexpensive, time saving method ofcutting quartz, (b) one which permits the use of smaller, andconsequently cheaper mother crystals in the production of piezoelectricand optical elements, and one which ensures minimum wastage of material.

The invention will be better understood from the following descriptionconsidered in connection with the accompanying drawing and its scope isindicated by the appended claims.

In the drawing wherein like reference characters designate the same orcorresponding parts in all figures,

Figure 1 is a view in outline and in perspective of a quartz mothercrystal cut, in accordance with the prior art, in planes normal to itsoptic (Z) axis, to provide a plurality of sections,

Figure 2 is an elevational view of one of the sections of Fig. 1 showingsubsequent cutting operations dictated by the later described prior artmethod of producing so-called V-cut piezoelectric quartz elements,

Figure 3 is a view in perspective of a quartz mother crystal which ismarked to indicate another prior art method of cutting V-cutpiezoelectric elements therefrom,

Figure 4 is a view in perspective illustrating subsequent cuttingoperations required by this prior art method,

Figure 5 is a view in perspective of a quartz mother crystal having cuttherefrom (in accordance with the present invention) a single bar whoselong dimensions are substantially parallel to the optic axis,

Figure 6 is a view in perspective of the bar of Fig. 4 removed and cutinto a number of semifinished V-cut piezoelectric blanks,

Fig. 7 is a View in perspective of one of the blanks of Fig. 6, and

Fig. 8 is a view in perspective of the bar of Fig. 4 removed and cutinto a number of semifinished X-cut and Y-cut piezoelectric blanks.

The term V-cut as used herein designates any crystal element whosethickness dimension is inclined at other than a right angle with respectto the optic (Z) axis of the mother crystal. The orientation of V-cutcrystals of both the thickness mode and contour mode" types aredescribed in considerable detail in British Patent 457,342 (1936).

The term X- cut or Curie cut as herein used designates any crystalelement whose thickness dimension lies along an X axis of the mothercrystal.

The term Y-cut or Tillyer-cut as used herein designates any crystalelement whose thickness dimension lies along a Y-axis of the mothercrystal.

The term Z-cut as used herein designates any crystal whose thicknessdimension lies along the optic (Z-axis) of the mother crystal. As isknown in the art, Z-cut crystals exhibit substantially no piezoelectricefiect, but may, when suitably ground and finished, be employed asoptical lenses and the like.

In accordance with one widely used method of cutting V-cut, X-cut,Y-cut, and Z-cut crystal elements. the practice has been to cut as manyslabs from the mother crystal in planes normal to the optic axis as thelength of the crystal and the ultimate desired size of the finishedelement will permit. This is indicated in Fig. 1 of the drawing, whereinthree sections I, 2 and 3, respectively, each, say, one-inch thick areshown cut from a mother crystal Q, whose optic axis is marked Z--Z. Fromthese sections l, 2 and 3, bars 4 (Fig. 2) whose short dimensions may beparallel to an X-axis or to an X+0 axis are cut. From the bars 4, thecrystal elements 5 are cut at an angle determined by the particularcharacteristic desired. Thus, referring to Fig. 2, if a V-cut crystalelement having a zero or some low temperature coeflicient of frequencyis required, the elements 5 may have their electrode faces inclined notonly with respect to the Z axis and with respect to the major (M) andminor (N) apex faces but also with respect to the X-axes, all asdescribed in detail in the above-mentioned British Patent 457,342.

One very real objection to the above described prior art method ofcutting quartz is that it can not be practiced economically with mothercrystals of small size (e. g. quartz candles" up to, say, mothercrystals will result in the production of numerous useless fragmentsunless the mother crystal is carefully selected with a finished elementof particular size in mind. In the case of the mother crystal hereillustrated, the fragments 6, I and 8, or some of them, may be used inthe production of very small piezoelectric elements (e. g. filtercrystals) but are usually discarded in commercial production because ofthe difliculties incident to the identification of the natural axes ofsuch fragments. Another objection to this method of the prior artresides in 2 diameter) and, in the case of larger the fact that thewastage at the areas 6, 1 and 8, Fig. 2, is duplicated in each centralsection I, 2 and 3. Further, each section and each bar 4 must beseparately set up in the cutting machine before the separatesemi-finished elements 5 can be realized. 7

Referring to Figs. 3 and 4, in accordance with another prior art methodof cutting ,V-cut blanks. the mother crystal Q is first sliced, at thedesired angle with respect to the Z-axis, into as many as possible slabsID of a thickness approximating that of the finished elements. The

principal objection to this method is that each.

thin slab H) must be separately set .up in the cutting machine in themanufacture of the semi finished blanks ll (Fig. 4). Another difficultywhich is especially apparent in the cutting of blanks of the indicatedorientation is that in at-- I tempting to practice this methodeconomicallythe corners l2 of the blanks may extend to the side faces Mand Not the mother crystalwhere imperfections (such as twinning) in thecrysbut little material need be removed from these semi-finished .blankstoprovide finished piezoelectric element of the desired dimensions thefinishing operation may be accomplished by grinding .or lapping andwithout setting up the separate blanks in a sawor other cutting machine.w 7

It will. be observed that. the principal wastage in material resultingfrom thepractice of this method is. that which occurs at 23, 24, Fig.'7, adjacentthe side faces of the mother crystal .where,. as abovepointed out, imperfections in the quartz are most likely to be present.It will alsoJ-be noted that there are. but .two end portions 5 and .26,(Fig. 6:) to be discardedinstead of six as in the .case of the method ofFigs. 1 and 2.

There is another very real saving incident to the practice ofthe/present. method in that it permits. the economical use of mothercrystals whose diameterissubstantially no greater than the diameter .ofthe elements to becut therefrom. v'I'heimportance of this. feature .ofthe invention will be appreciated by a reference to the .current priceof quartz. The price .of: raw quartz candles, of a size. suitable forthe cutting of blanks 11" square: in accordance with the presentinvention is currently about $4.00! per 1b.; the lar er pieces usuallyemployed in practicing prior methods cost up to 5316.00.13.81 1b.

While the invention has thus far as applied :to. the cutting of a--V.cut piezoelectric element, the electrode faces. of which aresubstantially parallel. to an X-axis and inclined at an angle (theactual angle .of the V-cut blanks of Figs. 2,. .3, 6 and 7 issubstantially 49) with respect in the optic axis in a directiontowardparallelism with av major. (M) apex face of the mother crystal, itwill be apparent the invention is, ,not'limited tothe cutting of crystalbeen described elements, useful for optical purposes, may be obtainedfrom the elongated bar of Fig. 5 by cutting it in planes normal to theoptic axis, in-' stead of askew with respect to it, as in the case ofthe V-cu elements 2| shown in Fig. 6. Such a Z-cutelement is shown at21, Fig. 6.

Referring to Fig- .8. In applying the invention 7 to the cutting ofX-cut and Y-cut blanks, the

bar 20 is'cut-in a direction parallel to the Z-axis so that, in the caseof an X-cut blank, its thickness dimension is parallel to an X-axis and,in

the. case of a Y-cut blank, the thickness dimension is parallel to aY-axis.

lOthehmOdificatiohg of the. invention will suggest themselve v.to :thoseskilled in the art. It is to be understood therefore thatv the foregoingis to :be interpreted. as illustrativeand not in a limiting sense exceptas requiredby the prior art and by the spirit of the appended claims.

What is claimed is:

LIMethOd of cutting a quartz crystal element from'natural quartz whichcomprise cutting directly from a mother crystal a bar whose longdimensions .aresubstantia'lly parallel to the optic axis and thencutting saidelement from said bar.

2. Method of cutting .a .quartz element from natural quartz whichcomprises cutting directly from a mother crystal 2. bar whose longdimensions are substantially parallel to the opticaxis and then cuttingsaid element from said barin planeswhich are transverse with respect tosaid optic axis.

3. Method of cutting a quartzpiezoelectric element from natural .quartzwhich comprises cutting. directly from a mother crystal a .barwhose longdimensions are substantially parallel to the optic axis and thencutting. said piezoelectric element from said bar at a desired anglewith re.- spect to said optic axis.

:4. Method of cutting a *V-cut quartz. piezoelectric element fromnatural. quartz which comprises cutting directly from a mother crystal abar whose long dimensions are substantially parallel .to the optic axis.and then cutting said elementirom saidbarat an acute angle with respectto said optic axis.

. 5. h/Iethod of cutting a quartz piezoelectric element from natur lquartz which comprises cutting directly from a mother crystal a barwhose vlong dimensions are substantially parallel to the optic axis andwhose short dimensions are only slightly greater than is required toproduce a finished element of the required dimensions, then cutting aslab from said bar at a desired angle with respect to said optic axis,.and finally reducing the dimensions of said slab to the desireddimensions of said element.

B;'M&l7h0d of cuttingja. Z-cut crystal ,element from natural quartzwhich comprises cutting directly from a mother crystal a bar whose lonadimensions are substantially parallel to the optic axis and thencutting said element from said bar at arig ht angle with respect to saidoptic axis.

1 CHARLES JOHNSON...

